This invention pertains to amber polyester compositions which are suitable for producing containers for food and beverages wherein blockage of ultraviolet and visible light is important. More specifically, this invention pertains to amber polyester compositions capable of absorbing significantly light of wavelengths shorter than about 550 nanometers (nm), which is achieved by a novel combination of a plurality of colorants, some of which may be copoylmerized into the polyester.
Polymers useful in the manufacture of containers for beverages and food in must possess a challenging combination of properties and technical specifications. For example, for containers intended for the packaging of carbonated beverages, the polymers used to produce the containers must prevent an excessive loss of carbonation through the walls of the container and must limit the ingress of oxygen to a very low level. Also, with some foods and beverages it is very desirable to protect them from ultraviolet light (UV) and some wavelengths of visible light.
The provision of polyester compositions useful for the manufacture of containers for beer is particularly challenging. Although a few beers are specifically treated to be resistant to light-induced changes, most beers are highly sensitive to light. As a result, the container or package must block the damaging portions of the light spectrum. The light-induced changes that occur to produce the characteristic light-struck or xe2x80x9cskunkyxe2x80x9d flavor are well documented, for example by J. Templar, K. Arrigan, and W. J. Simpson, Brewer""s Digest, Vol. 70, no. 5, pp 18-25 (1995) and references therein. It is generally accepted that not only ultraviolet light but also visible light of wavelengths shorter than about 550 nm is responsible for the formation of the light-struck flavor (Vita Biundo, Master Brewers Association of the Americas Technical Quarterly, Vol. 37, no. 2, pp. 233-238, and J. Templar, K. Arrigan, and W. J. Simpson, Brewer""s Digest, Vol. 70, No. 5, pp 18-25 (1995).). It is therefore desirable that polymers intended for use in the packaging of beer block a large portion of ultraviolet and visible light with wavelengths of less than about 550 nm from reaching the beer. This light protection may be accomplished by the addition of UV light absorbers and/or colorants. However, for packaging food and beverages it is essential that the colorants and/or other additives not extract, migrate or exude from the polyester composition into the contents of packaging articles manufactured from the polyester composition.
Polyesters having colorants and other light-absorbing compounds admixed and copolymerized therein are known. U.S. Pat. No. 4,617,373 discloses the use of certain copolymerizable methine dyes at concentrations from about 1 to 5,000 ppm in condensation polymers including an amber poly(ethylene terephthalate) formulation. However, the light protection provided by the disclosed formulation is not effective for light protection requirements over the 320-400 nm and 400-550 nm wavelength ranges (Comparative Example 1). U.S. Pat. Nos. 4,617,374, 4,707,537, 4,749,773, and 4,749,779 disclose polyester compositions comprising poly(ethylene terephthalate) having copolymerized therein certain benzylidine methine type UV-absorbing compounds, but do not mention the use of these methine UV absorbing compounds to produce a light-protected, amber-colored polyester.
U.S. Pat. No. 4,521,556 discloses amber polyester compositions comprising poly(ethylene terephthalate) containing certain yellow and red anthraquinone colorants copolymerized in the polyester. However, the compositions disclosed provide insufficient light protection for beer, particularly in the wavelengths from about 360 nm to 430 nm and at wavelengths from about 460 nm to 550 nm (Comparative Example 2). U.S. Pat. No. 4,745,173 discloses polyester compositions comprising poly(ethylene terephthalate) containing 1 to 20,000 ppm of colorants having the 2,5-diarylaminoterephthalate chromophore. The ""173 patent mentions the use of such orange colorants in the production of amber colored polyester, but does not mention any specific formulations that meet the light protection required for the packaging of beer. Experimentation has shown that the diarylaminoterephtalate chromophore inherently has a low extinction coefficient (absorptivity) and that high loadings or concentrations of colorants are required to block the blue spectral light at wavelengths of about 450 to about 490 nm when those colorants are combined with other colorants, such as yellow and red colorants, to produce the required amber color. These copolymerizable colorants containing the 2,5-diarylaminoterephtalate residue also lack the thermal stability needed for copolymerization into polyester at the upper range of temperatures usually encountered in the preparation of polyesters, e.g. temperatures above about 285xc2x0 C.
U.S. Pat. No. 4,359,570 discloses the use of copolymerizable yellow and red anthraquinone colorants as colorants in polyesters for food and beverage packaging. Again, the possible use of such colorants in an amber formulation is mentioned, but no specific combination of colorants for the production of an amber polyester suitable for packaging beer is given.
We have developed an amber polyester composition that absorbs a significant amount of light of wavelengths shorter than about 550 nm and is particularly suitable for use in the production of containers or other packaging materials intended for the packaging of materials that are susceptible to degradation by light of wavelengths shorter than about 550 nm. The amber polyester compositions are especially suitable for use in the manufacture of bottles for the packaging of beer. Accordingly, the present invention provides an amber polyester composition comprising a thermoplastic, molding grade polyester containing at least one compound, or the reacted residue of at least one compound, of each of Components I, II, and III and optionally IV wherein Components I, II and III have the formulas: 
and the Component IV Compound(s) are one or more phthalocyanine compounds; wherein
R is hydrogen, C1-C8-alkyl, or xe2x80x94(CH2CH2O"Parenclosest"n1xe2x80x94CH2CH2xe2x80x94X wherein n1 is 1-3 and X is a polyester reactive group selected from hydroxy, carboxy, C2-C6-alkanoyloxy and C2-C6-alkoxycarbonyl;
R1 is hydrogen or 1-2 groups selected from C1-C6-alkyl, C1-C6-alkoxy or halogen;
R2 and R3 each is C1-C8-alkyl, C3-C8-alkenyl, C3-C8-alkynyl, C3-C8-cycloalkyl or aryl; R2 and R3 in combination may represent a divalent group such as pentamethylene, ethyleneoxyethylene or ethylenesulfonylethylene; or R2 in combination with R1 may form an N-substituted 1,2,3,4-tetrahydroquinolin-6-yl ring, i.e., the residue having the structure: 
includes 1,2,3,4-tetrahydroquinoline radicals having the structure: 
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from hydrogen and C1-C6 alkyl;
R4 is C1-C8-alkyl;
R5 and R6 each is hydrogen or one to two groups selected from C1-C6-alkyl, C1-C6-alkoxy and halogen;
R7 is hydrogen, "Parenopenst"CH2CH2O"Parenclosest"n1xe2x80x94CH2CH2xe2x80x94X wherein n1 and X are defined above or C1-C6-alkyl;
R8 is hydrogen or one or two groups selected from C1-C6-alkyl, C1-C6-alkoxy and halogen;
R9 and R10 each is hydrogen, C1-C6-alkyl, C3-C8-cycloalkyl or aryl;
P is cyano, C1-C6-alkylsulfonyl, arylsulfonyl, aryl, heteroaryl, xe2x80x94CO2R11 and xe2x80x94CON(R12)R13, wherein R11 is C1-C6-alkyl, C3-C8-alkenyl, C3-C8-cycloalkyl and aryl; R12 and R13 each is independently selected from hydrogen, C1-C6-alkyl, C3-C8-cycloalkyl, C3-C8-alkenyl and aryl;
Q is one of the groups in the preceding definition of P;
L is an organic di-, tri- or tetravalent linking group;
L1 is an organic divalent linking group;
L2 is an organic divalent linking group;
n is an integer from 1 to 4;
m is an integer from 2 to about 50; and
m1 is 0, 1 or 2.
The phthalocyanine compound may be unmetallized phthalocyanine or metalized phthalocyanine, e.g., wherein the metal of the metal phthalocyanine is copper, iron, zinc, sodium, nickel, manganese, magnesium, lithium, cobalt and the like.
The compounds of Components I, II, and III are thermally stable and may be added during the polymerization process used in the preparation of the molding grade polyester to produce a polyester having the compounds polymerized therein or reacted therewith due to the presence of a polyester-reactive group on the compounds. Alternatively, the compounds of Components I, II and III may be admixed with the thermoplastic polyester by melt blending and extrusion methods when the compounds have molecular weights of at least about 450, which avoids the unwanted problems of the compounds being subject to extraction, exudation or subliming from the amber colored polyester compositions. Similarly, the phthalocyanine component may be added during polymerization or by melt polymerization after preparation of the polyester.